As a method of forming a film on a substrate, e.g., a semiconductor wafer (hereinafter referred to as a “wafer”), a method called an ALD (Atomic Layer Deposition) method and an MLD (Multi Layer Deposition) method (which will be collectively referred to as an ALD method) are conventionally used. The ALD method may provide a dense thin film and generally used for obtaining a good implantation property. In the ALD method, a specified film is formed by sequentially supplying different kinds of reaction gases reacting with one another to a wafer held within a process chamber.
In general, during a film-forming process, a film is deposited not only on a wafer but also on an inner wall of a process chamber. If the thickness of the deposited film grows larger, it causes the generation of particles. For that reason, a cleaning process is performed after films are formed on a predetermined number of wafers. The cleaning process is carried out by, e.g., supplying a highly-corrosive cleaning gas into the process chamber. The deposits adhering to the inner wall of the process chamber is detached from the inner wall when the deposits are contacted with the cleaning gas. While most of the detached components are removed by evacuating the interior of the process chamber, some of the detached components may sometimes remain within the process chamber. Thus, a purge gas is supplied into the process chamber and residues remaining within the process chamber are removed by conveying them out of the process chamber together with the flow of the purge gas.
After performing the cleaning process and the circulation of the purge gas, a wafer is carried into the process chamber and is subjected to a specified film-forming process. However, the particles may adhere to the wafer during the film forming process. Presumably, the reason is that the cleaning residues existing within the flow path of a deposition gas are supplied to the wafer together with the deposition gas along when the deposition gas circulates within the process chamber.
In respect of a particle reducing process, there is disclosed a related art in which an inert gas of a specified flow rate is introduced together with a reaction gas when processing a wafer and an inert gas of a large flow rate is introduced as a purge gas when performing a particle reducing process. In this related art, however, the flow path of the inert gas and the flow path of the reaction gas are independent of each other. Therefore, if the particles exist in the flow path of the reaction gas, it is likely that the particles adhere to the wafer when the reaction gas is supplied to the process chamber. There is also disclosed a related art in which, when an inspection item relating to a gas line connected to a process chamber is checked during the inspection of a semiconductor device, a purge gas is allowed to flow through the gas line at a maximum flow rate. In addition, there is disclosed a related art in which a gas is supplied in a pulse form by installing a pressure control tank in a gas supply pipe, installing a manometer in an exhaust pipe of the pressure control tank and controlling the internal pressure of the tank with the manometer to become a predetermined pressure.
There is disclosed a related art in which, when performing a film forming process, the internal pressure of a chamber is detected and the opening/closing operation of a valve is checked based on the detected internal pressure. There is also disclosed a related art in which a reaction gas tank provided with a manometer is installed in a flow path of a reaction gas and a plasma treatment is performed by supplying a reaction gas pre-filled in the reaction gas tank into the process chamber. In this method, if the volume of the process chamber is large, it is possible to rapidly supply the reaction gas such that the internal pressure of the chamber becomes a predetermined pressure. However, the related arts remain silent on a method of reducing particles by circulating a purge gas. It is therefore difficult for the related arts to solve the problems pointed out in the present disclosure.